Those skilled in the arts of antenna arrays and beamformers know that antennas are transducers which transduce electromagnetic energy between unguided- and guided-wave forms. More particularly the unguided form of electromagnetic energy is that propagating in “free space,” while guided electromagnetic energy follows a defined path established by a “transmission line” of some sort. Transmission lines include coaxial cables, rectangular and circular conductive waveguides, dielectric paths, and the like. Antennas are totally reciprocal devices, which have the same beam characteristics in both transmission and reception modes. For historic reasons, the guided-wave port of an antenna is termed a “feed” port, regardless of whether the antenna operates in transmission or reception. The beam characteristics of an antenna are established, in part, by the size of the radiating portions of the antenna relative to the wavelength. Small antennas make for broad or nondirective beams, and large antennas make for small, narrow or directive beams. When more directivity (narrower beamwidth) is desired than can be achieved from a single antenna, several antennas may be grouped together into an “array” and fed together in a phase-controlled manner, to generate the beam characteristics characteristic of an antenna larger than that of any single antenna element. The structures which control the apportionment of power to (or from) the antenna elements are termed “beamformers,” and a beamformer includes a beam port and a plurality of element ports. In a transmit mode, the signal to be transmitted is applied to the beam port and is distributed by the beamformer to the various element ports. In the receive mode, the unguided electromagnetic signals received by the antenna elements and coupled in guided form to the element ports are combined to produce a beam signal at the beam port of the beamformer. A salient advantage of sophisticated beamformers is that they may include a plurality of beam ports, each of which distributes the electromagnetic energy in such a fashion that different beams may be generated simultaneously.
Antenna arrays are becoming increasingly important for communication and sensing. Those skilled in the design of antenna arrays know that the physical size of the elemental antennas of the array and their physical spacing in an array is an inverse function of frequency, with higher frequencies requiring smaller antenna elements and spacings than lower frequencies. As it so happens, increasing bandwidths required for more sophisticated communications and sensing tend to result in the use of higher frequencies, with the result that the fabrication of antenna arrays tends toward fabrication of small structures arrayed with small inter-element spacings.
The problems associated with the fabrication of antenna arrays is exacerbated by the need which often occurs for the ability to radiate dual polarizations, which is to say the ability to selectively radiate or receive mutually orthogonal polarizations of electromagnetic energy. The ability to receive (and to transmit) significantly in a given polarization depends upon having a “radiating aperture” in the direction of the electric field of the desired polarization. Thus, an antenna, in order to be an effective, should have a finite (non-zero) dimensions (in terms of wavelength) in the direction of the electric field to be transduced. When dual polarization (or corresponding elliptical or circular polarization) is desired, the radiating elements must extend significantly in two mutually orthogonal directions.
The prior art relating to horn antenna arrays and their fabrication includes U.S. Pat. No. 6,891,511, issued May 10, 2005 in the name of Angelucci. The Angelucci method for fabricating an antenna array includes the placing an array of clips into a ground plane. The method also includes the “printing” of an array of electrically conductive horn antenna elements on a first dielectric circuit board (or set thereof), which first board(s) define a slot adjacent each antenna element. Such a printed board has a significant dimension only in one plane, so can only be an efficient radiator in the plane of the board. The first board(s) are mounted in a mutually parallel manner on the array of clips. A second dielectric board (or set of boards) is printed with similar conductive horns, but its slots are arranged to mate with the slots of the first board(s). The second boards are mounted onto the clips and the first board(s) so that, when mated, the second boards are mutually orthogonal to the first boards, and the horns form a rectangular array in which the antenna elements of the first boards radiate in a first polarization, and the antenna elements of the second boards radiate in a second polarization, orthogonal to the first polarization. The physical arrangement of the clips tends to stabilize the antenna array against deformation attributable to dimensional stability deviations of the dielectric materials.
Improved or alternative antenna arrays and methods for fabrication thereof are desired.